Here's a place where I can post my thoughts on new papers, provide updates on my projects, and post info that will eventually be on my website The Theropod Database - http://theropoddatabase.com/ . It will center on theropods, but may delve into other topics as well such as phylogenetics.

Tuesday, August 3, 2010

GSP's new taxon combinations from his dinosaur field guide

Taking a break from non-theropods, I checked out the Google Books preview for Gregory S. Paul's new The Princeton Field Guide to Dinosaurs. While I'm still disappointed in the basic layout of the book, I'm impressed by just how many new taxa Paul's managed to include, and the new skeletal reconstructions are awesome. As anyone who's read PDW should expect, Paul creates a ton of new genus-species combinations in this volume. Someone more well versed with sauropodomorphs and ornithischians will have to handle those clades, but what follows is a discussion of his new theropod names.

Abelisaurus garridoi- Instead of Aucasaurus. This could very well be true, but since Abelisaurus' skull was only described briefly and before other abelisaurids were recognized, and Aucasaurus' skull remains undescribed and schematically illustrated, it seems premature.

Allosaurus antunesi- Instead of Lourinhanosaurus. Now this one's problematic. Lourinhanosaurus has never even been hypothesized to be an allosaurid, and phylogenetic analyses suggest it is a more basal carnosaur or even a megalosauroid. Most recently, Benson et al. (2010) found it to be sister to Streptospondylus.

Streptospondylus nethercombensis- Instead of Magnosaurus. I should note that Paul also sinks Eustreptospondylus oxoniensis into Streptospondylus altdorfensis. The latter two species were placed as sister taxa by Allain (2002) and Smith et al. (2007) based on the presence of carotid processes in their anterior dorsal vertebrae, but it seems the feature is barely developed in Eustreptospondylus (Sadlier et al., 2008). The superior analysis of Benson et al. (2010) found Streptospondylus to be closer to Lourinhanosaurus, and a carnosaur instead of a megalosauroid. Sadlier et al.'s and Benson's recent papers have shown Rauhut's (2003) proposed relationship of Eustreptospondylus to Magnosaurus isn't as close as he thought, so sinking Eustreptospondylus without sinking Duriavenator and such seems unwise.

Carcharodontosaurus carolinii- Instead of Giganotosaurus. It turns out Paul was not the first to publish this combination, that honor going to Figueiredo, 1998, but the latter is so muddled that Paul can be said to be the first to competently publish it. ;) In any case, this is one of those subjective decisions. The problem is that most analyses agree Mapusaurus is closer to Giganotosaurus than to Carcharodontosaurus. So to sink Giganotosaurus you'd need to sink Mapusaurus too.

Monolophosaurus wucaii- Instead of Guanlong. Er, this I seriously doubt. I know Carr (2006) proposed Guanlong is a juvenile Monolophosaurus, but Paul doesn't think this is true. They don't emerge as closely related in any analysis except for Carr's (e.g. Rauhut's, Benson's).

Struthiomimus edmontonicus- Instead of Ornithomimus. Paul's given up his PDW synonymization of all ornithomimid genera, but edmontonicus is a junior synonym of brevitertius, and there is no evidence this species is closer to Struthiomimus than to Ornithomimus, Anserimimus or Gallimimus for instance.

Caudipteryx yixianensis- Instead of Similicaudipteryx. The problem here is that all the proposed similarities with Caudipteryx are symplesiomorphies. Similicaudipteryx shares some synapomorphies with caenagnathids in my analysis, though the new specimens could affect this.

Citipati barsboldi, gracilis, huangi and mongoliensis- Instead of Nemegtomaia, Conchoraptor, Heyuannia and Rinchenia. Synonymize derived oviraptorid genera if you like, but Conchoraptor has priority over Citipati. Paul seems to think Conchoraptor gracilis and "Ingenia" yanshini are synonyms, so yanshini should be the name he uses for that species. Where's Khaan you ask? A juvenile of Citipati osmolskae according to Paul. I bet Jaime will have some harsh words for these synonymies.

Sinornithosaurus ashile, lujiatunensis and zhaoianus- Instead of Shanag, Graciliraptor and Microraptor. Much like the previous example, making all microraptorians one genus is a subjective choice. Yet Hesperonychus was not sunk, and there is no evidence it's outside the clade formed by the above species. Shanag's placement as a microraptorian is also questionable. Another issue is that Richardoestesia is extremely similar to Sinornithosaurus and Shanag, but would have priority if all of these genera were synonymized. Better to keep them separate in my opinion.

Velociraptor mangas- Instead of Tsaagan. This is problematic since Tsaagan was most recently placed as sister to Adasaurus (Longrich and Currie, 2009) or as basal to Eudromaeosauria (Senter, 2007).

These examples indicate the general problems with synonymizing Mesozoic dinosaur genera. I agree Mesozoic dinosaurs are oversplit compared to recent taxa, and I've been a big proponent of synonymizing species (Alioramus altai, Didactylornis jii, etc.). But when it comes to genera, you first have to be sure they form a monophyletic group. I'd say most of Paul's new combinations fail at this. Even if they do form a clade, you run the risk of having an earlier-named genus ending up in it. Richardoestesia as a microraptorine was an example above, and Suchosaurus is another if you want to sink Cristatusaurus into Baryonyx. This makes our current monospecific dinosaur genus trend more stable. And even if you have a perfectly stable clade of species, you have to ask yourself what the point of synonymization is. Paul's Carcharodontosaurus is already Carcharodontosaurinae, his Sinornithosaurus is already Microraptoria. So it doesn't increase the ease of communication, and it misleadingly implies a similarity greater than that between other sister genera. Are Microraptor and Sinornithosaurus more similar to each other than Achillobator is to Utahraptor, for instance? Who can say? All you end up doing is forming instability compared to past publications and sinking a name someone else published.

Paul, 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press. 320 pp.

True, but in the species' actual entry it's listed as "Giganotosaurus (or Carcharodontosaurus) carlinii". Paul does this quite a bit, with "Conchoraptor (or Citipati) gracilis" and "Velociraptor (or Tsaagan) mangas" as other examples.

Is this actually Paul's doing? I'm well aware of Paul's fondness for informal taxonomic lumping and all for holding the GSP POPSCI Juggernaut accountable to scientific scrutiny. These...um revisions, however, just seem far too sloppy for even Paul. Its almost like some over zealous editor went through the book and attempted to make the book more accessible to the the lay public by synonymizing every thing with a more famous relative.

Giganotosaurus being sunk down to Carcharodontosaurus? That's completely unnatural, a more likely way (a lumper's way, anyway) would to sink Mapusaurus into Giganotosaurus.I'd also like to ask: If I lumped Bistahieversor into Albertosaurus (which I do, I'm kind of a Pauline lumper) would that effect Appalachiosaurus in any way?

I agree, and indeed Mapusaurus was first announced as a species of Giganotosaurus.

As for the tyrannosaurids, it all depends on your phylogeny. In Carr's various published phylogenies Appalachiosaurus is outside Tyrannosauridae and Bistahieversor is a basal tyrannosaurine. So in these topologies I think your lumping would be wrong, assuming you agree with the consensus that taxa should be monophyletic. My website takes Carr's published phylogenies (which are basically cranial-only) and adds his hindlimb characters from the Alectrosaurus analysis in his thesis. In that case, Appalachiosaurus and Bistahieversor are both albertosaurines. And then I'd say lumping to make Albertosaurinae into Albertosaurus is a subjective opinion.

My question to you is- what benefit does your lumping accomplish? Since "genus" is completely subjective, your taxonomy is no more true than the consensus taxonomy. Even if you could prove that sealeyi and libratus were more similar to each other than two congeneric mammal species are, nobody cares. Similarity-based taxonomy is an archaic system that's dying out in dinosaur paleontology as its practitioners do. Just like non-cladistic phylogenetic analyses, it has no future in the field. All it does when you call Bistaheiversor Albertosaurus sealeyi is confuse people.